Introductory book that focuses on the essentials of Lisp programming and discusses the "bottom up" paradigm for program design. This well organized introduction to the language also serves as a useful reference. Shortly after Paul Graham wrote ANSI Common Lisp, he and his friend Robert Morris used Lisp to create Viaweb, a web-based application that was acquired by Yahoo in 1998.

Other excellent Lisp books

Practical Common Lisp (Peter Seibel)

Another good introductory book with more emphasis on how Common Lisp is used for real projects. Includes many example projects, including web application development.

On Lisp (Paul Graham)

Picks up where ANSI Common Lisp left off, covering advanced topics in more detail. This book is full of techniques that other languages aren't capable of matching.

Paradigms of Artificial Intelligence Programming (Peter Norvig)

Starts with an introduction to the language, including an excellent discussion of programming style. Most of the book is a collection of projects covering classic topics in Artificial Intelligence. This book also includes many examples in Prolog.